App build for Apple & Android - location-based & elegant

I'm looking to build a straight-forward but elegant mobile app for the city I live in. It's primary aim is to guide visitors and locals to shops that I rate highly - helping them to find good quality with ease. Every year hundreds of thousands of visitors come to my city as tourists so there's a real opportunity to guide them via a map with marked sites and location services. Other attributes of these shops would also be listed and searchable to help users make their way to the right shop for their needs. I'd like users to be able to save shops as favourites, search by key word and share the shops they like via email, twitter, facebook and text message. I'm particularly interested in the process/costs of updating the app when new shops open (i.e. can I do it myself or are we entering into an ongoing arrangement that requires you to update for me?) and the process/costs involved in updating the app when Apple and Android update their operating systems. I'm looking for a reliable and trustworthy partner who will take the time to get the app right so that it is sustainable ongoing - not just a quick job that may cause problems down the line. I'm also open to starting simple and adding on other functionality over time so process/cost outline for this will also be key to the successful partner. I'm looking to choose three quotes and then catch up over Skype/facetime to talk it through before choosing a partner. Previous work you've done that is similar will be a distinct advantage. I want realistic quotes and a realistic assessment of costs. I'm based in the UK.